Disc storage systems are known in the art and are used to storage information for later retrieval. Such disc storage systems include a rotating disc which carries information thereon. A transducing head (or, in some instances, a readback head) is positioned over a surface of the disc while the disc rotates at high speed. The head is carried on a slider which is designed to "fly" just over the surface of the rotating disc. The head may then be used to write information onto the disc, or read information from the disc. Such information may be, for example, magnetically encoded on the disc surface.
Increased storage density is becoming increasingly important. Optical data storage systems are a promising technology for storing large quantities of information. The information is accessed by focussing the laser beam or other light source onto a data surface of the disc and analyzing light reflected from or transmitted through the data surface. In general, in optical storage systems, data is in the form of marks carried on the surface of the discs which are detected using the reflected light. There are a number of different optical disc technologies which are known in the industry. For example, compact discs are currently used to store digital data such as computer programs or digitized music. Typically, compact discs are permanently recorded during manufacture. Another type of optical disc is a write-once read-many (WORM) system in which a user may permanently write information onto a blank disc. Other types of systems are erasable such as phase change and magneto-optic (M-O) systems. Phase change systems detect data by sensing a change in reflectivity. M-O systems read data by measuring the rotation of the instant light polarization due to the storage medium.
In order to increase storage density, the transducing head must be positioned very close to the disc surface, for example, on a slider which flies over the disc surface. Further density improvements may be obtained by coupling, the light to the disc surface using the near field, as opposed to the traditional far field technique. Such near field recording is described in U.S. Pat. No. 5,125,750 to Corle et al. which issued Jun. 30, 1992 and in U.S. Pat. No. 5,497,359 to Mamin et al. which issued Mar. 5, 1996. These optical recording systems use a solid immersion lens (SIL) which is carried on a slider and positioned just over the disc surface for near field recording. With recording at such high density and with the transducing head in such close proximity to the optical disc, even slight variations in this precise configuration can lead to recording errors or head crashes.